Structural Arrangement of Myosin

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The general structure of the myosin filament has been known since the classical x-ray diffraction studies of Huxley and Brown (1963). However, one of the crucial features, namely, the filament ordering or the number of myosin cross-bridges per 143 Å repeat, has been controversial throughout (Squire, 1981). Analysis of myofibrillar proteins by means of one-dimensional sodium dodecyl sulfate polyacrylamide gels has yielded conflicting results. This author reinvestigated the myosin to actin stoichiometry from one-dimensional gels of myofibrils prepared by different procedures. Next, this author addressed the critical issue of whether the differences in actin concentration during the different methods of muscle preparation were a result from loss of actin or removal of contaminants that comigrate with actin. In examining this question, two-dimensional electrophoresis, sodium dodecyl sulfate in the first dimension and isoelectric focusing in the second dimension were performed on myofibrillar preparations of rabbit muscle. Results revealed a structural arrangement of myosin cross-bridges in vertebrate striated muscle.